(1) Field of the Invention
This invention relates to a process for producing a magnetic recording medium. More particularly, it relates to a process for producing a magnetic recording medium exhibiting an enhanced durability against wear due to sliding contact of the magnetic hard disc (hereinafter referred to as "HD") with a magnetic head.
(2) Description of the Related Art
The recent progress of increasing the density of magnetic recording mediums is remarkable. It was said before that the rate of density increase of hard disc drives (hereinafter referred to as "HDD") is about 10 times per 10 years, but now it may be said that the rate of density increase is about 100 times per 10 years.
In HDD, there is adopted mainly a Winchester system, i.e., CSS (contact start-stop) system involving a basic operation of a sliding movement due to contact of HD with a magnetic head, flying of the head and then a sliding movement due to contact of HD with the head. The CSS system has contributed in no small measure to the amazing progress in increase of recording density. However, this system has invited an attractive problem of tribology. Namely, the amazing progress in increase of recording density has invited an increase of rotational speed of the disc and a reduction of flying height of the magnetic head. Thus, there is now an increasing demand for improving head-and-disc wear characteristics and stability in sliding movement, and for enhancing smoothness of the HD surface.
The key to the improvement of head-and-disc wear characteristics lies in an increase of the tenacity of materials and a lowering of friction coefficient or an enhancement of lubrication. As regards HD, attempts have been made for lowering the friction coefficient by rendering rough the HD surface, and for coating the HD with a protective coating material such as diamond-like carbon (DLC) or a coating lubricating agent. The surface treatment for lowering the friction coefficient is referred to as a "texture treatment" and is intended to effectively reduce the contact area in the CSS system whereby the head-and-disc wear characteristics are improved. The texture treatment comprises forming peaks and indentations or valleys having predetermined height and depth on the textured HD surface, and now the texture treatment is an essential step for the HD production.
The texture treatment greatly depends upon the particular material of the disc substrate. For example, in the case of a nickel-phosphorus (Ni--P)-coated aluminum substrate, the surface roughening is effected by mechanical grinding using an abrasive grain. In the case of a glass substrate, etching techniques utilizing lithography or a combination of lithography with printing have been proposed and a part thereof have been practically adopted.
In the texture treatment, there are problems inconsistent with each other, i.e., it is difficult to precisely control the surface roughness with an enhanced production efficiency. Namely, the mechanical grinding has technical problems of over-grinding or burr formation, and blurring of textured areas, and the lithographic etching has a problem that the production steps are complicated.
In recent years texture treatments utilizing laser beam such as laser ablation and laser etching have attracted attention (see, for example, U.S. Pat. No. 5,062,021 and Japanese Unexamined Patent Publication No. 62-209,798). The laser beam texturing is advantageous in that the surface roughness can be precisely controlled and the production steps are conducted in a dry state without use of a liquid. The kinds of laser beams, wavelengths and energy densities are selected depending upon the particular material of the substrate treated.
When the laser beam texturing is conducted for substitute substrates such as glass and silicon substrates, if the kinds of laser beams, wavelengths and energy densities are not appropriately selected, it is highly possible that flied powders are undesirably deposited or over-etching occurs with the results that cracks are caused and the CSS characteristics are deteriorated.